1. Field of the Invention
The present invention relates to a method and a device for separating submicron particles mixed into liquid. The present invention particularly relates to a method and a device for separating particles, the method and the device being appropriately applied to a micro total analysis system (Micro-TAS), a micro electro mechanical system (MEMS), and the like, in which analytical chemistry and micro chemistry technologies are integrated into a palm-size chip in thermal fluid mechanics, electrochemistry, and analytical chemistry on a micro/nano scale by use of a micromachine technology.
2. Description of the Related Art
The research and development of Lab-on-a-chip and Micro-TAS which are conceived to become large industry in a few years, that is, a palm-size device into which an experiment, analysis and the like at a conventional laboratory level are integrated is rapidly conducted. Many micro channels, the width of which is from several tens μm to several hundreds μm, are disposed in this device, and it is desired that the analysis of a little liquid sample, the reactive synthesis of a chemical agent and the like be effectively and rapidly carried out. A device to make a blood test, a DNA judgment operation, or the like possible has already been on the market in actuality. It is expected, on the other hand, to make the device further multifunctional, and especially it is deeply desired to establish technology for selectively separating particular particles and a particular material existing in a liquid sample.
Until now, the separation operation of the submicron particles existing in the analyzed liquid sample (in a buffer solution, in general) is generally carried out with the use of a large-scale centrifugal separator. In this method, it is possible to precisely separate and extract the particular particles by use of a filter which is smaller than the diameter of the objective particle. Thus, this method has been positively used in the field of analytical chemistry and the like. It is difficult, however, to add a centrifugal separation function to the device for the purpose of rapidly carrying out a series of chemical reaction operations in the device, so that there is a problem that the device is complicated.
Therefore, focusing attention on the viewpoint of thermal fluid mechanics, separation technologies using rheological properties in the device are developed in recent years. An H-filter (Paul Yager et al., MicroTAS 1998 proceedings, 202-212), being one of the separation technologies, which separates the particles or the material existing in the buffer solution by use of difference in a diffusion coefficient of the particles or the material, has an advantage that external mechanical driving force is not necessary.
The development of a cell sorter are also carried out (Anne Y. F. et al., Nature 1999, Vol. 17, 1109-1111). In this technology, the particles to be separated are impregnated with a fluorescent material, and are monitored with a sensor and separated by rheological switching control, and the like.
Furthermore, Japanese Patent Laid-Open Publication No. 2002-233792 proposes a method in which a solution including the particles flows through a channel and a voltage is applied at the midpoint of the channel so as to generate an electric field in the direction of crossing the channel. The particles are attracted by the generated electric field and captured on this side in the channel.
The H-filter, however, cannot completely separate the particles and the material by a single operation due to its principle. The addition of a particle separation function such as, for example, the centrifugal separation function makes the structure of the device complicated. The cell sorter, on the other hand, is hard to use for the particle separation operation in a field with high concentration such as an actual rheological field. Furthermore, the method disclosed in Japanese Patent Laid-Open Publication No. 2002-233792 has a problem that the method cannot separate the particles with enough efficiency.